In many applications it is important to differentiate between the bulk properties of a material or device and the surface properties of that material or device. The bulk or substrate material provides a set of bulk properties suitable for the intended application, such as mechanical properties or refractive properties. However, in many applications the surface properties of the substrate material are not suitable or ideal for the intended application. Accordingly, for these substrate materials surface modification is required to modify the surface properties of the substrate.
Surface modification techniques include methods such as adsorption, self-assembled monolayer (SAM) formation, functionalised silanes, Langmuir-Blodgett deposition, layer-by-layer (LbL) assembly, and covalent attachment of genetically-engineered surface-binding peptides. These techniques have limitations for widespread practical use. For instance, adsorbed coatings may desorb under certain conditions, which limits the appropriateness of adsorption as a surface modification technique in a variety of applications. Furthermore, simple adsorption is not readily applicable to a large variety of substrate materials, as the properties of the substrate are not suitable for attracting and retaining the coating polymers. Whether the properties of a substrate are appropriate will also depend on the type of polymer that is to be applied. Although covalent surface modification techniques improve adhesion, chemical specificity between interfacial modifiers and substrates (eg alkanethiols on noble metals and silanes on oxides) is typically required. The substrates and polymers available for surface modification chemistry is the primary limitation.
LbL derived coatings (Decher G. “Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites”, Science, 277, 1232-1237 (1997)) can be reliably and evenly deposited from aqueous solutions, provide good adhesion and control over the coating thickness while providing functional groups that can be used for subsequent surface immobilisation reactions and can be used for coating various substrate geometries such as porous materials and internal surfaces in a device. However, LbL assembly requires a multi-step procedure for implementation.
It would be helpful to have a simpler one-step process that provides a multi-purpose, polymeric coating that may be used in chemical, biological and material sciences, as well as in applied sciences, engineering and technology. It is desirable that the process not be limited by the substrate material or geometry and that the process has the capability to be carried out (i) under either oxidative or non-oxidative conditions, (ii) in aqueous or non-aqueous solutions, and (iii) in the gaseous phase.
Lee et al suggest that dopamine goes some way to that solution (Lee, H. et al, “Mussel-Inspired Surface Chemistry for Multifunctional Coatings”, Science, 318, 426-430 (2007)). Neutralisation of the dopamine hydrochloride salt at high pH generates the free dopamine which then spontaneously polymerises to give a polydopamine coating. However, dopamine derived coatings require oxidative conditions for implementation. In addition, dopamine derived coatings are limited to liquid solution based chemistries.
The present invention seeks to ameliorate the deficiencies of the prior art in providing coatings of widespread applicability and practicality of use. Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.